The present invention relates to the provision of structures for the adequate drainage of liquids by artificial means and has particular application in the area of landscape gardening and/or the provisions of grass standings or verges. Further embodiments of the invention relates to an improved drainage system for traffic areas such as roadway, train corridors and runways.
Known methods of draining water from relatively large surface areas where the funnelling of water directly into narrow diameter pipes is impractical or impossible, involve the use of a layer of stone or gravel capable of supporting the surface to be drained. Water from this xe2x80x9cgravelxe2x80x9d layer ay then be allowed to percolate into the ground below, follow the lie of the land through said gravel to further conventional drainage channels or pipes or is otherwise evacuated.
Where the area to be drained is a roof-top garden for example, and the roof top is of concrete, the concrete may be covered with a water impervious membrane; the membrane serving to shed water into conventional channels, gutters or drains. Over the membrane there may be a layer of pebbles that is in turn covered by drainage structure in the form of a generally flat filter of a material known as geotextile material. Finally, a layer of soil is laid in which vegetation may be grown is applied over the filter.
The layer of pebbles facilitates drainage of water from the soil to enable adequate oxygen to reach the roots of vegetation therein, and the filter prevents the soil from clogging the layer of pebbles, which would prevent drainage. The lower impervious membrane prevents the ingress of moisture to the building or structure below.
The above described use of pebbles, or gravel or stone in place of the pebbles, bas been found to have various defects. Firstly, such a system may be expensive insofar as stones or pebbles, which are heavy, present transportation problems both in terms of moving them to the site and to lifting them when at the site. Also, the supporting structure may need reinforcing to support the pebbles or the stones. The pebbles may puncture the impervious membrane due to sharp edges and/or excessive weight. The above described system does not permit the deployment of water or power or other conduits within the system, particularly where such conduits are to be put in after the drainage system has been laid.
In European Patent No. 0244651 it set forth a drainage structure that addresses these problems, and overcomes them by providing that a drainage structure is of generally flat configuration and is cellular in nature, so that water (or other liquid or gas) can pass through it in any direction which means either in a direction transverse to the plane of the structure or in a direction in the plane of the structure.
The structure disclosed in said European Patent comprises a pair of plate members having apertures therein, held in spaced relation by means of spacer members so that there are formed cells, which are hydraulically interconnected with each other, between the plate members. When the structure is in use, it will normally be horizontal or substantially so, and to induce the water flowing through the structure to pass between the cells, the apertures of the top plate member are offset relative to the apertures of the bottom plate member.
As, also shown in the European Patent, at the lower ends of the spacer members, are connecting walls that extend between adjacent spacer members. These walls retain some water in the bases of some of the cells to a level to the tops of the walls, and in use the water eventually cascades over the walls into adjacent cells where there are apertures in the lower plate member, and the water then flows out of the apertures and out of the structure. In so cascading, the water makes some splashing, which in turn adds to the oxygenation of same, improving the quality of the draining water.
The present invention, in one form, is concerned with this aspect of the prior draining structure, and seeks to improve this oxygenation. Of the draining water even further and to thereby improve its quality, although it is not necessary that the draining structure of the present invention have all of the specified features of the prior structure, even although they are preferred.
According in one form, the present invention comprises a draining structure which is generally flat in nature and is for use mainly in a horizontal or substantially horizontal disposition, and comprises top and bottom plate members which are held spaced apart by spacer members so that the structure is cellular in nature with the cells hydraulically interconnected with each other, the plate members having apertures therein which are disposed so that the apertures in the top plate member are offset relative to the apertures in the bottom plate member, and wherein there are web walls extending between adjacent spacer members at the lower plate member and form at their top edges, weirs for water which is retained by the web walls, wherein the top edges of the web walls are curved, notched or otherwise shaped or the walls have apertures, to cause the water spilling over these edges into adjacent cells at a varying velocity profile to increase the oxygenation of the water as it splashes on falling from the weir top edges.
Preferably, the web walls are provided adjacent the top and bottom plates, so that the structure is usable equally well either way up, i.e., with either plate upmost. The said edges are preferably curved edges and may be defined by circular, oval or other continuously curving shapes formed in which are webs connecting adjacent spacer members.
This form of the invention provides for better oxygenation of the water passing through the structure whereby its quality can be improved, simplifying disposal into the municipal draining system, and there is the added advantage that the web walls can be such as to provide better resistance of the structure it shear forces applied in the plane of the structure and compression forces applied transverse to the plane of the structure. Shearing can happen in use by virtue of ground movements, especially where the structure is use on sloping ground, and compression loading can occur where the structure is used in circumstances where live loads such as vehicle traffic can be expected.
As in the prior structure, the structure is preferably a one piece moulding of plastics material, although for larger areas, several of the structures can be clipped together by virtue of formations on the structures themselves, or by other means.
It is to be mentioned that the invention is not limited in its use to roof-top gardens. It can be used to provide drainage under roadways, under embankments and elsewhere where drainage is required and /or where surface erosion might be a problem. For instance in car parks or pervious roads to mitigate flood or contaminated waters from roads or highways, the structure can be used as a pervious paving combination with pervious soils and/or plants such as turf. The structure can be designed to allow heavy loads to be impressed thereon without damaging the plant material.
According another form, the present invention comprises a liquid pervious layer support which is generally flat in nature and is for use mainly in a horizontal or substantially horizontal disposition, and comprises top and bottom plate members which are held spaced apart by spacer members so that the structure is cellular in nature with the cells in communication with each other, the plate members having support areas alternating with apertures in a checkerboard arrangement, the apertures are disposed therein so that the apertures in the top plate member are offset relative to the apertures in the bottom plate member, each support area having an opening therein and wherein there are web walls extending between adjacent spacer members at the lower plate member and form at their top edges, weirs for water which is retained by the web walls, wherein the top edges of the web walls are curved, notched or otherwise shaped or the walls have apertures, to cause the water spilling over these edges into adjacent cells at a varying velocity profile to increase the oxygenation of the water as it splashes on falling from the weir top edges.
Preferably the web walls are formed on both the top and bottom plate members.
Other pervious paving on the market has been unsuccessful because of the small capacity of the pervious drainage element and the heat absorbed by the concrete that burns or dehydrates the grass. Other plastic paying does not allow the natural horizontal and vertical growth of the root system of turf. In the case of this structure it allows the natural horizontal growth of the turf root systems, protecting other materials in the system, such as the lining material, from compaction due to the road traffic.
The system will, preferably, require a drainage structure beneath the root zone at a depth of approximately 300 mm to ensure sufficient moisture capacity to allow the robust growth and recovery of the turf.
The invention also extends to a drainage system embodying a structure as aforesaid and a method of drainage using a drainage structure as aforesaid.
Presently the roadways arc based upon the old Roman system of having a water impervious top layer that directs water into side gutters where it passes into underground pipes and drains, which are impervious to water, and is directed from a large catchment area into creeks, rivers and the ocean.
Thus when it rains, all of the rubbish and pollution such as oil, grease, vegetation, dog faeces, food stuffs, paper and detergents, are flushed into the drainage system and concentrated into the outfall area, such as a creek, river and the ocean. There is little or no attempt in most of the existing drainage systems to decontaminate this pollution. If any treatment is carried out, it, usually, only involves a filtering out of larger solids. This dumping of the stormwater runoff into the water ways, depletes the oxygen from the waterways, and introduces chemicals which increases, in some cases exponentially, the growth algae, both of which destroys the healthy fauna and flora of the waterways.
Further because the natural water absorbing soils and vegetation have been covered or removed and replaced by water impermeable roads, there is an increase in the amount of runoff in urban areas, than if the area was in its natural state.
Additionally the use of bitumen and concrete on the roads causes a heat sink to absorb and retain the solar energy and in a small way contribute to the heating of the planet.
The present invention, in another form, seeks to ameliorate these problems by providing a roadway or other transport corridor drainage system comprising:
at least the edge surface of the roadway or other transport corridor, being permeable to water, such that water can flow therethrough;
a permeable drain located at least below said permeable edge surface; and
a water permeable retention tank connected to said permeable drain, such that runoff passes through the permeable surface into the permeable drain and into the permeable retention tank, where the water is stored and flows back into the soil through the walls of the tank.